Drying apparatus



Jan. 25, 1944. R. E; CLARKE DRYING APPARATUS Original Filed Dec. 17 19405' Sh eets-Sheet 1 INVENTOR Kobe/f C/ane ATTORNEY Jan. 25', 1944. R. E;CLARKE 2,339,979

DRYING APPARATUS Original Fil d Dec. 17. 1940 3 Sheets-Sheet 2 INVENTOR2090/ C/ane ATTORNEY R. E; CLARKE DRYING APPARATUS Jan. 25, 1944.

Original Filed Dec. 17, 1940 3 Sheets-Sheet 3 I INVENTO R ,abef/ A. /aneATTORNEY Patented Jan. 25, 1944 DRYING APPARATUS Robert E. Clarke. PaloAlto, Calif assigllor to Marine Magnesi um Products Corporation,

South San Francisco, Calif., a corporation of Delaware Originalapplication December 17, 1940, Serial No. 370,475. Divided and thisapplication January 13, 1942, Serial No. 426,598

Claims. (01. 259-9) This invention relates generally to drying apparatusapplicable to the production of dry products from aqueous pastes orslurries. The invention has been advantageously applied to the drying ofwet slurries of magnesium products, particularly slurries of magnesiumcarbonate and magnesium hydroxide.

It is an object of the invention to provide an improved form of dryingapparatus of the above character, particularly with respect to the meansemployed for feeding the wet slurry to the drying belts.

A further object of the invention is to provide an improved form offeeder for drying apparatus, capable of distributing strings of amaterial like magnesium hydroxide or magnesium carbonate slurry,uniformly and continuously upon a drying belt.

Additional objects of the invention will appear from the followingdescription in which the preferred embodiment has been set forth indetail in conjunction with the accompanying drawings. The presentapplication is a division of my copending application, Serial No.370,475, filed Dec.

' belt to the main drying belt;

Fig. 5 is a side view, partly in cross section, showing the feedingapparatus which is incorporated with the drier;

Fig. 6 is an end view of the. apparatus shown in Fig. 5;

Fig. 7 is a cross sectional detail taken along the line 1-1 of Fig. 5;

Fig. 8 is a view like Fig. 7 but showing the parts in a differentoperating position; 1

Fig. 9 is an enlarged cross. sectional detail showing the dischargenozzles; and

Fig. 10 is a bottom plan view of the nozzles as shown in Fig. 9.

The complete drying apparatus diagrammatically illustrated in Figs. 1 to4, inclusive, consists of a drying chamber A, which encloses the twodrying belts B and C. The special feeding apparatus D supplies materialto the belt B, and

partially dry solid material from this belt is transferred to belt C forfinal drying. The special feeding apparatus D is constructed to supplystrings of slurry to the belt B, and these strings while being traversedby movement of the belt are dried a sufilcient amount to form solubleand self-supporting sticks which are then deposited indiscriminatelyupon the belt 0.

- Figs. 5 tom, inclusive, illustrate the details of the preferred typeof special feeding apparatus. Referring particularly to Figs. 7 and 8,the exterior end of belt conveyor B is'shown engaging the roller i2.Belt B, as well as belt C, can be formed of suitable inaterial such assections of woven wire netting. Roller I2 is shown mounted by having itsends provided with shaft extensions l3, engaged by the journal blocksll. Guide tracks l6 and ll slidably mount the journal blocks ll, andthese tracks in turn are carried by the support members l8. Threadedrods l9 ,are attached to blocks i4 and facilitate making adjustments ofthe positioning of the blocks to secure proper tensionmg of conveyor B.

In order to deliver paste to the upper run of the conveyor, 1 provide achamber 20 which is conveniently in the form of a cylinder, and whichextends horizontally across the conveyor. The ends of this chamber areprovided with flanges 2i to which the end walls 22 are secured. Thepaste or slurry to be handled by the apparatus is applied to theinterior of chamber 20 through two or more openings 23, which aredistributed along the length of the chamber. In practice, a paste orslurry of material such as magnesium carbonate or magnesium hydroxidecan be handled by a suitable form of positive displacement pump whichhas its discharge side connected to the inlet 23 through suitableflexible hose connections. As will be presently explained, flexible hoseconnections are desirable in order to make possible tilting movement ofchamber 20.

The lower side of chamber 20 is provided with a plurality of dischargenozzles 24. It is desirable that each nozzle be in the form of a tube ofsuitable length, and it is also desirable to have the tubes staggered asshown in Fig. 10. In handling material like a magnesium carbonateslurry, it is satisfactory to utilize tubes'about 2 inches long, andhaving an internal passage of about 3% of an inch in diameter.

Within chamber 20 I provide means for forcing a relatively uniform flowof material through the several discharge nozzles. This means ispreferably an agitator in the form of a wiper wheel 26, which consistsof a tubular shaft 21, provided continue to flow through the nozzles.

witha plurality of circumferentially spaced vanes 28. The outer endportion 29 of these vanes are formed of flexible material such as stripsof fabric reenforced vulcanized rubber.

For mounting agitator 26, the ends of the same have shaft extensions 3i,which are carried by end journals 32. These journals are mounted uponthe end plates 22, and are provided with suitable glands 33 to avoidleakage. Note (Fig. 'l) that the axis of rotation of agitator 26 iseccentric with respect to the central axis of chamber 26. For the normalposition of chamber 20, the axis of rotation is somewhat below the axisof the chamber, so that the flexible D 1' ons29 engage the inner wallsurface of the chamber in a region about the inlets of nozzle 24. Inother words, these flexible elements wipe across the inlets of thenozzles as the agitator is rotated. One of the shaft extensions 3! isprovided with a suitable sprocket wheel 34, which in turn is engaged bya suitable drive chain from a variable speed motor, for driving thewheel at a suitable rate. For different slurries, the rate of rotationmay vary, as for example from 20 to 65 revolutions per minute.

For the normal position for the parts shown 'in Fig. 7 the nomles 24deliver material to the upper run of the conveyor. At certain times itis desirable to interrupt the supply of material to the conveyor, eventhough some material may To make this possible, I have provided a typeof mounting for chamber 20, so that this chamber can be tilted to such aposition that material flowing through the nozzles no longer isdischarged upon the conveyor. Thus the supporting brackets 36 for thechamber 20 are provided with rollers 31 and 38, which support chamber26, and thus permits the chamber to betilted about its axis. To preventlongitudinal movement of the chamber, rollers 36 are shown provided withgrooves engaged by the circular track 39. Tilting of chamber 20 to anangle of approximately 45 from the position shown in Fig. '7, issufficient to transpose the nozzles 24 to a' position as shown in Fig.8, where material discharged from the nozzles falls past the ends of theconveyor, to be received by launder 412 Instead oi-tiltingchamber 20 byhand, it can be connected to a suitable tilting motor for remoteoperation. Thus as shown in Fig. 6,0ne end of chamber 20 can be providedwith a. sprocket 42 engaged by the chain 43. A smaller sprocket 44engaged by chain 43 can connect to the shaft of a reversible electricmotor. For automatically controlling this motor so that the chamber willbe stopped automatically in either one of two operating positions, Ihave shown limiting switches 46 and 41 attached to the adjacent bracket36, and each provided with trip rollers 48 and 49. A cam segment ismounted upon the chamber adjacent the sprocket 42 and serves to engagethe trip rollers 48 and 49 as the chamber is tilted from one position toanother. Thus when current is supplied to the driving motor by closing aremote switch and when the chamber occupies the normal position of Fig.7, the chamber tilts in a counterclockwise direction as viewed in Fig.7, until the cam segment 5| contacts roller 49 of limiting switch 41,and then the supply or current to the motor is automatically interruptedwith the chamber finally coming to rest in the position shown in Fig. 8.Upon again closing the circuit to the motor, the motor drives thechamber in a reverse direction so that the chamber finally comes to restback in the position of Fig. 7.

Operation of the feeding apparatus described above can be reviewed asfollows: Assuming that the parts are positioned as shown in Fig. 7, andthat the conveyor belt is operating at a predetermined speed, thematerial to be dried is pumped to the chamber through the openings 23.Initially there will be insuflicient pressure to force any appreciableamount of material through the nozzles 24. However, as the level of thematerial within the chamber 20 rises, the trapped air above thismaterial is placed under pressure, and this pressure in turn tends toforce more material through the nozzles 24. By adjusting the rate atwhich-the material is pumped to the chamber, the level of the materialwithin the chamber can be adjusted to a value desired, so that there isa pressure within the chamber adequate for feeding the material at thedesired rat through the nozzles. For example, when handling an aqueousslurry of magnesium carbonate containing about 12 to 15% magnesiumcarbonate, the chamber can be maintained about A full, with an internalpressure of about 0.5 pound per square inch. Air at higher pressures canbe supplied to the upper portion of the chamber to force thickermaterial through the nozzles.

The agitator 26 is driven at a constant rate, as for example 34revolutions per minute, in handling magnesium carbonate slurry; As thewheel rotates, it performs several functions, all of which aid insecuring the results desired. It serves to recurrently wipe off theentrance or inlets of the nozzles, and thus prevents these nozzles frombecoming clogged by removing any securing thorough intermixture withresulting uniformity.

As disclosed in said co-pending application Serial No. 370,475, as thematerial is discharged from nozzles 24' it is carried away upon theupper run of the conveyor B in the form of a series of parallel strings.The speed of the conveyor is adjusted in order to prevent the stringsfrom becoming too thick 'or too thin. Strings which are too thick makefor inefficient drying and may cause adjacent strings to contact andmerge together. Strings which are too thin make for ineificientoperation of the drier and seriously reduce the capacity of theequipment. When it is desired to interrupt the supply of material to theconveyor belt, as for example at the end of a run, one simply tilts thechamber to the position shown in Fig. 8 so that material flowing outthrough the nozzles 24 drips down into launder 4|.

The remaining structural features of the dryer have been disclosed in myaforesaid co-pending application, Serial No. 370,475. Briefly, thedrying chamber enclosing conveyor B is divided into compartments 6| and62. The remainder of the chamber enclosing conveyor C is divided intocompartments 63, 64 and 65. Each compartment is provided withcirculating blowers or fans 61 and with heaters 66 which can utilizesuitable fuel gas. Each circulating fan (Figs. 2 and '3) has its inletopening 69 communicating with the space below the upper run of conveyorC at one side of the drying chamber, and a short discharge conduit Iextends upwardly from the blower and discharges into the side space II,from which the drying as flows outwardly and downwardly over the heaters68. Each heater II is in the form of a tube or metal conduit with oneend communicating. through the side wall of the drying chamber andprovided with a burner 12. The other end of the burner unit is incommunication with space 13 which is isolated from the main space of thedrying chamber by the horizontal and vertical walls I4 and 16. Below thelower edge of wall 16, space 13 communicates with the space below theupper run of the conveyor belt (Fig. 2) A flue pipe 18 provided with avalve or damper, communicates with space 13 and makes possible thedrawing in of a controlled amount of atmospheric air. Exhaust pipe 19communicates between the exterior and space II to permit the continualexhaust of moisture-laden air to the atmosphere.

To review operation of the apparatus as a whole, it will be presumedthat one wishes to dry an aqueous slurry of basic magnesium carbonatecontaining about 13% solids. The feeding apparatus D is operated aspreviously described to discharge parallel strings of the slurry uponthe upper run of the conveyor belt B, substantially as shown at Si inFig. 4. While being transferred through the compartments 6i and 62,these strings of wet material are contacted with the drying gas so thatthe moisture content is reduced to such an extent that the stringsbecome relatively solid and friable. Various temperatures can be used,as for example a drying gas temperature in compartments iii and 62 offrom 350 to 400 F. The material mentioned is suflloientiy solid andfriable to transfer to belt 0 when the solids content is increased toabout 25%.

At the inner discharge end of conveyor 3, the strings break into selfsupporting sticks of material which are dropped and piledindiscriminately upon the upper run of conveyor C. Scraper 82 can beemployed to aid proper discharge upon conveyor B. Conveyor C is operatedat a relatively slow speed compared to conveyor B, as for exampleconveyor B can be about 25 feet long and can travel at about feet perminute, while conveyor C can be about 60 feet long and can travel at aspeed ofabout 1 foot per minute. Thus the sticks of material 83 arepiled upon the upper run of conveyor C to form a bed of considerabledepth through which the drying gas may circulate (Fig 4).

When the material is delivered from the end of the conveyor C, itsmoisture content has been reduced to the value desired. At thisdischarge end a suitable scraper blade 84 can be provided, and thematerial can be delivered through the discharge chute 85. The driedmaterial can then be ground to form a powdered product of the desiredfineness.

Iclaim:

1. An apparatus for continuously feeding strings of a thick slurry upona receiving surface, a closed horizontally extending chamber positionedover said surface, a series of discharge nozzles along the underside ofthe chamber, means for supplying slurry under pressure to the chamber tomaintain a body of slurry of substantial depth within the chamberoverlying the discharge nozzles and to maintain air under pressure abovesaid body, means for agitating the slurry in said chamber and aidingflow of slurry through the nozzle, said means comprising a plurality ofrotatable wiping elements within the chamber for wiping over the inletsto said nozzles, an means for rocking the chamber together with saidagitating means to displace said nozzles from a position for dischargeof material on said surface to a second position in which the materialis discharged oil of said surface.

2. An apparatus for continuously feeding strings of a paste or thickslurry upon a receiving surface, a closed cylindrical horizontallyextending chamber positioned over said surface adapted to receive thepaste, a plurality of discharge nozzles communicating through theunderside of the chamber, means for supplying said paste to said chamberunder pressure to provide a body of said paste of substantial depth oversaid nozzles and to maintain air under pressure above said body, a wiperwheel rotatably disposed within the chamber for agitating said paste andaiding flow of said paste through said nozzles, the wiper wheel havingan axis of rotation disposed below the longitudinal axis of the chamber,said wiper wheel being provided with a plurality of flexible wipingelements for contacting and wiping over a segmental portion of thechamber wall through which said nozzles communicate, and means formounting said chamber for rocking movement about its axis to displacesaid nozzles from a position for discharge of material on said surfaceto a second position in which the material is discharged oil of saidsurface.

3. An apparatus for continuously feeding strings of a thick slurry upona conveyor or belt, a closed elongated chamber extending horizontallyover one end of the conveyor, a series of discharge nozzles along theunderside of the chamber, means for supplying slurry under pressure tothe chamber to provide a body of said slurry of substantial depth withinthe chamber overlying the discharge nozzles with a space above said bodycontaining air under pressur greater than atmospheric, means foragitating the slurry in said chamber and aiding substantially continuousand uniform flow of slurry through the nozzles, said means comprising aplurality of rotatable wiping elements disposed within the chamber forwiping over the inlets of said nozzles, and means for rocking thechamber together with said agitating means to displace said nozzles fordischarging material beyond said end of said conveyor.

4. An apparatus for continuously feeding strings of a thick slurry upona conveyor, an elongated chamber extending horizontally over one end ofthe conveyor for receiving said slurry, a series of discharge nozzlescommunicating through one side of the chamber, rotatable wiping andagitating means within the chamber for aiding flow of slurry through thenozzles, journal means for said wiping means secured to end walls of thechamber and mean for rocking the chamber together with said wiping meansto displace said nozzles for discharging material beyond said end of theconveyor.

5. An apparatus for feeding strings of a thick slurry upon a receivingsurface, a cylindrical shaped chamber for receiving said slurryextending horizontally over said surface, said chamber having end walls,a plurality of nozzle communieating through one side of said chamber,wipins and agitating means within the chamber for aiding flow oi slurrythrough the nozzles, said, wiping means having an axis of rotationeccentric with respect to the longitudinal axis of the chamber. .Iournalmeans on said end walls for said wiper means, and means for mountingsaid chamber for rocking-movement about its axis to displace saidnozzles from a position for discharge of material on said surface to asecond position in which the material is discharged oi! or said 5surface.

ROBERT E. CLARKE.

